Formation of graphene-encapsulated CoS₂hybrid composites with hierarchical structures for high-performance lithium-ion batteries

Abstract

Transition metal sulfides (TMSs) are considered as the most promising alternative anode materials for advanced lithium-ion batteries (LIBs). Here, we report a hierarchically structured CoS 2 nanosphere/graphene (CoS 2 /G) composite, fabricated by a simple hydrothermal method. This composite, assembled with CoS 2 nanoparticles uniformly distributed on the graphene, exhibits excellent electrochemical performance. In particular, the CoS 2 /G electrode material delivers a high rate capability of around 398 mA h g À1 at a current density of 3500 mA g À1. Moreover, a discharge capacity of about 400 mA h g À1 can be obtained after 1000 cycles at a current density of 500 mA g À1. X-ray absorption spectroscopy is used to characterize the sample for the first time, and the results demonstrate that CoS 2 /G is reduced to metallic Co and Li 2 S when discharged to 0.01 V. In subsequent charge-discharge processes, the metallic Co cannot be fully oxidized to CoS 2 , which is the main cause of capacity loss for the CoS 2 electrode.

Conversion reaction of vanadium sulfide electrode in the lithium-ion cell: Reversible or not reversible?

“…35 Note that the spectrum at the end of discharge is still different from that of V metal, which may be related to the small domain size of the as formed metal clusters and/or the interaction between formed Li2S and V metal. [36][37][38] During the subsequent charge to 3.0 V, the intensity of the pre-edge peak increases and the main absorption edge shifts back to higher energies, indicating the recovery of the symmetry and the gradual oxidation of V atoms. Overall, the in situ and operando S and V K-edge XAS results clearly demonstrate that the electrochemical reaction of VS2 is reversible in the first cycle and both S and V are involved in the redox reactions during the electrochemical processes.…”

Understanding the electrochemical reaction mechanism of VS2 nanosheets in lithium-ion cells by multiple in situ and ex situ x-ray spectroscopy

“…35 Note that the spectrum at the end of discharge is still different from that of V metal, which may be related to the small domain size of the as formed metal clusters and/or the interaction between formed Li2S and V metal. [36][37][38] During the subsequent charge to 3.0 V, the intensity of the pre-edge peak increases and the main absorption edge shifts back to higher energies, indicating the recovery of the symmetry and the gradual oxidation of V atoms. Overall, the in situ/operando S and V K-edge XAS results clearly demonstrate that the electrochemical reaction of VS2 is reversible in the first cycle and both S and V are involved in the redox reactions during the electrochemical processes.…”

The application of nanostructured transition metal sulfides as anodes for lithium ion batteries

“…Simultaneously, some researches on the use of CoS 2 in LIBs have also been reported. Like other TMSs, limiting CoS 2 to various carbon materials is an effective way to improve its electrochemical performance, such as CNTs [94,95] , graphene [94,[96][97][98][99] and hollow C microspheres [100][101][102] . Furthermore, in order to explore the electrochemical behaviors and mechanism of CoS 2 during the charge anddischarge, Su et al [103] investigated its electrochemical process using in situ transmission electron microscopy.…”